The present invention relates generally to determining a state of health (SOH) of a rechargeable battery in a transportation vehicle.
A vehicle's electric power supply system must support a plurality of vehicle functions that operate on electric energy. Such functions include normal vehicle operation devices and safety related devices such as rear window defogger, anti-lock braking/stability systems, lighting systems, etc. In addition to these devices, the vehicle's electric power supply system supports comfort, convenience, and entertainment devices. Some examples include air conditioning, heated seats, video/audio systems, and accessory outlet convenience devices. With the advent of new X-by-wire technologies (e.g., steer-by-wire, brake-by-wire, etc.) even more electric power is being demanded of the vehicle's electrical power system.
The increasing use of electrical devices as described above directly affects the drain on the vehicle battery, and hence, the battery's useful life. The acceleration of battery aging has a direct correlation with the frequency of use of such devices, which uses the vehicle battery as their power source.
Moreover, hybrid electric vehicle applications utilize both electric drive systems and internal combustion engines. Such systems require more energy from a vehicle battery than a typical internal combustion engine system. The operating modes of hybrid vehicles are typically described as charge depleting or charge sustaining with reference to the battery pack. Some hybrids can be charged off an electrical grid, whereas most hybrids operating in a charge sustaining mode receive the electric charging from an alternator driven by the internal combustion engine. Therefore, hybrid systems use high power rechargeable batteries to meet the power requirement. With high power output and more frequent usage of the batteries, accurate and robust capacity estimation is needed for battery SOH monitoring to ensure reliable and safe operation of hybrid systems. In addition, an accurate capacity estimate can be further utilized to enhance state of charge estimation and electric power management.
A known method used to determine battery capacity measurements is to use a time-consuming full charging and discharging process in a laboratory environment which is not suitable for on-board vehicle applications.